The invention relates generally to methods and apparatus for obtaining formation evaluation logs. More specifically, the invention relates to a body for protecting sources and sensors used in measuring formation properties in a borehole environment.
Various well logging techniques are known in the field of hydrocarbon exploration and production. These techniques typically employ logging instruments or sondes equipped with sources adapted to emit energy through a borehole traversing the subsurface formation. The emitted energy interacts with the surrounding formation to produce signals that are detected and measured by one or more sensors on the instrument. By processing the detected signal data, a profile or log of the formation properties is obtained. Logging techniques known in the art include wireline logging, logging while drilling (LWD), measurement while drilling (MWD), and logging while tripping (LWT). Wireline logging involves lowering the instrument into the borehole at the end of an electrical cable to obtain the subsurface measurements as the instrument is moved along the borehole. LWD/MWD involves disposing the instrument in a drilling assembly for to obtain subsurface measurements while a borehole is drilled through subsurface formation. LWT involves disposing sources or sensors within the drill string to obtain measurements while the drill string is withdrawn from the borehole.
Sources and sensors used in making subsurface measurements are typically disposed in cylindrical sleeves or housings. The housing protects the sources and/or sensors from the borehole environment. For example, U.S. Pat. No. 4,873,488 (assigned to the present assignee) discloses a logging sonde including a support having a generally tubular shape. The support is made of a metal that is preferably non-magnetic and has excellent electrical conductivity. Transmitter and receiver coil units are located along the axis of the support. The coil units are insulated from the metallic material of the support by insulating sleeves. Holes are provided in the support for passage of electrical conductors connected to the coil units. The coils and support are installed in an insulating sleeve made of non-conductive material, such as fiberglass-reinforced epoxy, to protect the coil units from the mud in the borehole. U.S. Pat. No. 7,026,813 (assigned to the present assignee) describes a semi-conductive sleeve for subsurface use.
Throughout the development and advances in subsurface measurements, there continues to be a desire for a robust and inexpensive methodology for protecting sources and/or sensors in a borehole environment.